Fifteen years after American test pilot Chuck Yeager first broke the sound barrier, a new front opened in the Cold War. With the Americans and Soviets still engaged in an all-out sprint to win the Space Race, both sides of the Iron Curtain launched a battle for supersonic supremacy. Months before the British and French governments signed an agreement in 1962 to jointly develop the world’s first supersonic passenger aircraft, Soviet leader Nikita Khrushchev had secretly ordered his top aviation engineers to do the same.

While supersonic projects by American manufacturers Lockheed and Boeing became bogged down by budgetary and environmental concerns, the joint British-French Concorde venture became the leader in the supersonic race. The Soviets, who lagged years behind in engine and aviation technology, knew there was only one way to catch up—espionage.

The head of the Paris office of Soviet airliner Aeroflot, Sergei Pavlov, recruited a network of French Communist Party members and paid informants to infiltrate the Toulouse, France, factory of Concorde manufacturer Aerospatiale. Although the French deported Pavlov in 1965 after plans of the Concorde’s landing gear were found in his briefcase, for years afterwards secret agents continued to steal thousands of documents and blueprints in one of the largest industrial espionage operations in history. According to a declassified CIA report, the spy ring even included a pair of Czechoslovakian priests who helped to smuggle rolled-up microfilms of Concorde’s plans inside toothpaste tubes that were carried by spies posing as tourists on the Ostend-Warsaw Express. Inside the British Aircraft Corporation’s factory, an English spy codenamed “Ace” also allegedly funneled thousands of classified documents to the Soviets.

Thanks to the spy ring, the Soviets not only caught up with the West, they took to the skies three months before the Concorde’s first test run. On December 31, 1968, the TU-144 (named for the Tupolev Design Bureau that developed it) emerged from a secret hangar near a snowy Moscow airstrip and roared into the frigid sky on a successful 38-minute test flight. Just days after Apollo 8 had returned from orbiting the moon, the Soviets had their own propaganda coup. The photographs of the TU-144 splashed across the front pages of newspapers around the world shocked the Concorde’s designers. The sleek fuselage, needle nose and delta wings of the Soviet aircraft looked so similar to the Concorde that the press dubbed it the “Konkordski.”

After years of continued development, a redesigned TU-144, sporting a pair of insect wings behind the cockpit to assist with lift, arrived at the 1973 Paris Air Show for a supersonic showdown with the Concorde. On June 3, 1973, the Konkordski took to the skies immediately following a flawless demonstration by its rival. The crowd watched as the Soviet jet made a steep ascent before violently leveling off. The TU-144 then went into an abrupt dive, began to break up and crashed into a fireball that consumed a neighborhood in the village of Goussainville. The crash killed six crew members and eight people on the ground, including three children playing outside.

Authorities reported that the black box flight recorder was destroyed in the accident, and Soviet and French inquests blamed the pilot for the crash. In the years that followed, however, it was revealed that a French Mirage fighter plane had taken to the air moments before the supersonic jets in order to covertly take photographs of the TU-144 in flight. The Concorde’s pilot had been warned about the fighter jet. The TU-144’s pilot had not, in a breach of air show regulations. It has been speculated that the Soviet pilot was startled by the Mirage on his ascent and took drastic action to prevent a collision, which stalled the engines and caused the fatal tailspin. “It is my view that the Soviets and the French authorities cut a deal,” said U.S. intelligence analyst Howard Moon in a 1996 documentary produced for Britain’s Channel 4. The Soviets wouldn’t mention the presence of the Mirage if the French didn’t blame the crash on the TU-144’s structural failure.

The crash set back the Konkordski’s development, and it did not begin passenger service until nearly two years after the Concorde when it flew an Aeroflot route between Moscow and Alma-Ata on November 1, 1977. Only 17 of the TU-144 models were ever built, and its service was limited to domestic flights. Another test flight crash in May 1978 resulted in the suspension of the Konkordski’s passenger service after just a little more than 100 commercial flights. The TU-144 continued to fly cargo routes until it was finally grounded in 1983.

The Concorde, meanwhile, struggled through its own problems and never met its transformational promise. Only 20 of the aircraft were ever built—far fewer than the 200 projected in 1967—and it failed to make back the billions of dollars of tax money invested in it by the British and French governments. By the time the Concorde finally took flight in 1976, the Boeing 747 already ruled the skies and a global oil crisis had vastly increased the operating costs of the fuel-guzzling aircraft, which consumed a ton of fuel a minute at takeoff. Noise regulations and public protests about the Concorde’s sonic booms also forced it to fly at less than supersonic speeds except over bodies of water. A July 2000 crash of a Concorde just after takeoff in Paris that killed 113 people forced both Air France and British Airways to suspend service for a year. The Concorde returned two months before the September 11, 2001, attacks that sent aviation into a global slump, and the Concorde was retired by both airlines in 2003.

In the 1990s, after the collapse of the Soviet Union, America’s National Aeronautics and Space Administration (NASA) worked with Russian aerospace engineers to modify a TU-144 for use as a flying laboratory in a joint research program to develop a second-generation supersonic airliner. Although born out of the tensions of the Cold War, the Konkordski found a second life as an unlikely symbol of American-Russian cooperation.